The myb genes have been highly conserved during evolution. Three myb- related genes (c-myb, A-myb, and B-myb) have been identified in mammals, birds, and amphibians. The c-myb gene is essential for fetal hematopoiesis and altered forms of c-myb cause leukemias and lymphomas in mammals and birds. The Myb proteins are nuclear, bind to specific DNA sequences and regulate transcription. However, the critical genes that lie upstream and downstream in the myb pathway remain unknown. A Drosophila myb-related gene was first identified over ten years ago, but remains largely uncharacterized. We have shown that the Drosophila Myb DNA-binding domain recognizes the same DNA sequence as Myb proteins from vertebrates and from the cellular slime mold Dictyostelium discoideum. Furthermore, we have recently shown that segments of the Drosophila Myb protein can functionally replace homologous segments of the vertebrate v- Myb protein in oncogenic transformation. In addition, we have found that the homology among vertebrate Myb proteins and Drosophila Myb is more extensive than previously appreciated. The high degree of evolutionary conservation of other oncogene-related pathways among vertebrates, Drosophila, and the nematode Caenorhabditis elegans leads us to believe that the myb pathway may be similarly conserved. Therefore, we now propose to use the genetic and biochemical tools available in Drosophila and C. elegans in order to place myb within a genetic pathway. To accomplish this goal, we propose the following specific aims: 1. To determine the pattern and mechanism of regulation of myb expression in Drosophila during various stages of development; 2. To determine if the Drosophila Myb protein can function as a transcriptional regulator in tissue culture cells and in intact animals; 3. To create transgenic Drosophila in which the misexpression of wild type and/or mutant forms of Myb cause scoreable phenotypes; 4. To use these phenotypes to identify and order genes that enhance or suppress Myb function; 5. To identify target genes regulated by the Drosophila Myb protein; and, 6. To identify and characterize the expression of myb-related gene(s) and protein(s) in C. elegans.